Fuel for use in fuel cell

ABSTRACT

A fuel for a fuel cell system comprising 0.5-40 mass % of oxygenates in terms of an oxygen content based on the whole fuel. The fuel for a fuel cell system has a high power generation quantity per weight, a high power generation quantity per CO 2  emission, a low fuel consumption, a small evaporative gas (evapo-emission), small deterioration of a fuel cell system comprising such as a reforming catalyst, an aqueous gas shift reaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks and the like to maintain the initial performances for a long duration, good handling properties in view of storage stability and inflammability and a low preheating heat quantity.

TECHNICAL FIELD

The present invention relates to a fuel to be used for a fuel cellsystem.

BACKGROUND ART

Recently, with increasing awareness of the critical situation of futureglobal environments, it has been highly expected to develop an energysupply system harmless to the global environments. Especially urgentlyrequired are to reduce CO₂ to prevent global warming and reduce harmfulemissions such as THC (unreacted hydrocarbons in an exhaust gas),NO_(x), PM (particulate matter in an exhaust gas: soot, unburned highboiling point and high molecular weight fuel and lubricating oil).Practical examples of such a system are an automotive power system toreplace a conventional Otto/Diesel engine and a power generation systemto replace thermal power generation.

Hence, a fuel cell, which has high energy efficiency and emits only H₂Oand CO₂, has been regarded as a most expectative system to response torespond to social requests. In order to achieve such a system, it isnecessary to develop not only the hardware but also the optimum fuel.

Conventionally, as a fuel for a fuel cell system, hydrogen, methanol,and hydrocarbons have been candidates.

As a fuel for a fuel cell system, hydrogen is advantageous in a pointthat it does not require a reformer, however, because of a gas phase ata normal temperature, it has difficulties in storage and loading in avehicle and special facilities are required for its supply. Further, therisk of inflammation is high and therefore, it has to be handledcarefully.

On the other hand, methanol is advantageous in a point that it isrelatively easy to reform, however power generation quantity per weightis low and owing to its toxicity, handling has to be careful. Further,it has a corrosive property, special facilities are required for itsstorage and supply.

Like this, a fuel to sufficiently utilize the performances of a fuelcell system has not yet been developed. Especially, as a fuel for a fuelcell system, the following are required: power generation quantity perweight is high; power generation quantity per CO₂ emission is high; afuel consumption is low in a fuel cell system as a whole; an evaporativegas (evapo-emission) is a little; deterioration of a fuel cell systemcomprising such as a reforming catalyst, a water gas shift reactioncatalyst, a carbon monoxide conversion catalyst, fuel cell stacks andthe like is scarce to keep the initial performances for a long duration;a starting time for the system is short; and storage stability andhandling easiness are excellent.

Incidentally, in a fuel cell system, it is required to keep a fuel and areforming catalyst at a proper temperature, the net power generationquantity of the entire fuel cell system is equivalent to the valuecalculated by subtracting the energy necessary for keeping thetemperature (the energy for keeping balance endothermic and exothermicreaction following the preheating energy) from the actual powergeneration quantity. Consequently, if the temperature for the reformingis lower, the energy for preheating is low and that is thereforeadvantageous and further the system starting time is advantageouslyshortened. In addition, it is also necessary that the energy forpreheating per fuel weight is low. If the preheating is insufficient,unreacted hydrocarbon (THC) in an exhaust gas increases and it resultsin not only decrease of the power generation quantity per weight butalso possibility of becoming causes of air pollution. To say conversely,when some kind of fuels are reformed by the same reformer and the sametemperature, it is more advantageous that THC in an exhaust gas is lowerand the conversion efficiency to hydrogen is higher.

The present invention, taking such situation into consideration, aims toprovide a fuel suitable for a fuel cell system satisfying theabove-described requirements in good balance.

DISCLOSURE OF THE INVENTION

Inventors of the present invention have extensively investigated tosolve the above-described problems and found that a fuel comprising aspecific amount of oxygenates (oxygen-containing compounds) is suitablefor a fuel cell system.

That is, a fuel for a fuel cell system according to the inventioncomprises;

(1) 0.5-40 mass % of oxygenates therein in terms of an oxygen contentbased on the whole fuel.

The fuel comprising the specific amount of the oxygenates is preferableto satisfy the following additional requirements;

(2) the fuel contains 5 vol. % or more of hydrocarbons based on thewhole fuel;

(3) a content of hydrocarbon compounds having a carbon number of 4 is 15vol. % or less, the content of hydrocarbon compounds having a carbonnumber of 5 is 5 vol. % or more and the content of hydrocarbon compoundshaving a carbon number of 6 is 10 vol. % or more based on the wholehydrocarbons;

(4) distillation properties are the initial boiling point indistillation of 24° C. or higher and 40° C. or lower, the 10 vol. %distillation temperature of 25° C. or higher and 50° C. or lower, the 90vol. % distillation temperature of 45° C. or higher and 130° C. orlower, and the final boiling point in distillation of 55° C. or higherand 150° C. or lower;

(5) a sulfur content is 50 ppm by mass or less based on the whole fuel;

(6) saturates are 30 vol. % or more based on the whole hydrocarbons;

(7) olefins are 35 vol. % or less based on the whole hydrocarbons;

(8) aromatics are 50 vol. % or less based on the whole hydrocarbons;

(9) a ratio of paraffins in saturates is 60 vol. % or more;

(10) a ratio of branched paraffins in paraffins is 30 vol. % or more;

(11) heat capacity of the fuel is 2.6 kJ/kg ° C. or less at 15° C. and 1atm in liquid phase;

(12) heat of vaporization is 400 kJ/kg or less;

(13) Reid vapor pressure (RVP) is 10 kPa or more and less than 100 kPa;

(14) research octane number (RON, the octane number by research method)is 101.0 or less;

(15) oxidation stability is 240 minutes or longer; and

(16) density is 0.78 g/cm³ or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of a steam reforming type fuel cell systememployed for evaluation of a fuel for a fuel cell system of theinvention.

FIG. 2 is a flow chart of a partial oxidation type fuel cell systememployed for evaluation of a fuel for a fuel cell system of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the contents of the invention will be described further indetail.

In the present invention, the oxygenates mean alcohols having carbonnumbers of 2 to 4, ethers having carbon numbers of 2 to 8 and the like.More particularly, the oxygenates include methanol, ethanol, dimethylether, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether,tertiary amyl methyl ether (TAME), tertiary amyl ethyl ether and thelike.

The content of these oxygenates is required to be 0.5 mass % or more interms of an oxygen content based on the whole fuel in view of a low fuelconsumption of a fuel cell system as a whole, a small THC in an exhaustgas, short starting time of a system and the like, and further isrequired to be 40 mass % or below, preferably 20 mass % or below andmost preferably 3 mass % or below taking into consideration of a balancebetween a power generation quantity per weight and a power generationquantity per CO₂ emission.

Although the fuel for a fuel cell system of the invention may containonly oxygenates mentioned-above, the fuel is preferably a mixture ofoxygenates and hydrocarbons and it is more preferable that the amount offormulation for hydrocarbons is 5 vol % or more based on the whole fuelin view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission and the like.

Although the amount of hydrocarbon compounds having specific carbonnumbers contained in hydrocarbons is not restricted when the oxygenatesare mixed with the hydrocarbons in the invention, however, the followingrequirements are preferable.

Although the content of hydrocarbon compounds having a carbon number of4 is not restricted, the content of hydrocarbon compounds having acarbon number of (V (C₄)) shows the content of hydrocarbon compoundshaving 4 carbon atoms based on the whole hydrocarbons and is required tobe 15 vol. % or less since the evaporative gas (evapo-emission) can besuppressed to low and the handling property is good in view ofinflammability or the like and preferably 10 vol. % or less and mostpreferably 5 vol. % or less.

Although the content of hydrocarbon compounds having a carbon number of5 is not restricted, the content of hydrocarbon compounds having acarbon number of 5 (V (C₅)) shows the content of hydrocarbon compoundshaving 5 carbon atoms based on the whole hydrocarbons and is required tobe 5 vol. % or more because of a high power generation quantity perweight, a high power generation quantity per CO₂ emission, and a lowfuel consumption of a fuel cell system as a whole and preferably 10 vol% or more, more preferably 15 vol. % or more, further more preferably 20vol. % or more, much further more preferably 25 vol. % or more, and mostpreferably 30 vol. % or more.

Although the content of hydrocarbon compounds having a carbon number of6 is not restricted, the content of hydrocarbon compounds having acarbon number of 6 (V (C₆)) shows the content of hydrocarbon compoundshaving 6 carbon atoms based on the whole hydrocarbons and is required tobe 10 vol. % or more because of a high power generation quantity and alow fuel consumption of a fuel cell system as a whole and preferably 15vol. % or more, more preferably 20 vol. % or more, further morepreferably 25 vol. % or more, and most preferably 30 vol. % or more.

Although the content of hydrocarbon compounds having carbon numbers of 7and 8 are not particularly restricted in the invention, hydrocarboncompounds containing 20 vol. % or less as the (V (C₇+C₈)) in total basedon the whole hydrocarbons are preferably used.

Further, in the invention, the content of hydrocarbons having carbonnumbers of 10 or more is not particularly restricted, however, becauseof a high power generation quantity per CO₂ emission, a low fuelconsumption of a fuel cell system as a whole, and small deterioration ofa reforming catalyst to maintain initial performances for a longduration, the total amount of hydrocarbon compounds having carbonnumbers of 10 or more (V (C₁₀₊) based on the whole hydrocarbons ispreferably 20 vol. % or less, more preferably 10 vol. % or less and mostpreferably 5 vol. % or less.

Incidentally, the above-described V (C₄), V (C₅), V (C₆), V (C₇+C₈), andV (C₁₀₊) are values quantitatively measured by the following gaschromatography. That is, these values are measured in conditions:employing capillary columns of methyl silicon for columns; using heliumor nitrogen as a carrier gas; employing a hydrogen ionization detector(FID) as a detector; the column length of 25 to 50 m; the carrier gasflow rate of 0.5 to 1.5 ml/min, the split ratio of (1:50) to (1:250);the injection inlet temperature of 150 to 250° C.; the initial columntemperature of −10 to 10° C.; the final column temperature of 150 to250° C., and the detector temperature of 150 to 250° C.

Although the distillation properties are not particularly restricted inthe fuel of the invention, however, the following properties arepreferable. The initial boiling point (initial boiling point 0) ispreferably 24° C. or higher and 40° C. or lower, and more preferably 26°C. or higher. The 10 vol. % distillation temperature (T₁₀) is preferably25° C. or higher and 50° C. or lower, and more preferably 30° C. orhigher. The 90 vol. % distillation temperature (T₉₀) is preferably 45°C. or higher and 130° C. or lower, more preferably 100° C. or lower andfurthermore preferably 80° C. or lower. The final boiling point indistillation is preferably 55° C. or higher and 150° C. or lower andmore preferably 130° C. or lower and further more preferably 100° C. orlower.

If the initial boiling point (initial boiling point 0) in distillationis low, the fuel is highly inflammable and an evaporative gas (THC) iseasy to be generated and there is a problem to handle the fuel.Similarly regarding to the 10 vol. % distillation temperature (T₁₀), ifit is less than the above-described restricted value, the fuel is highlyinflammable and an evaporative gas (THC) is easy to be generated andthere is a problem to handle the fuel.

On the other hand, the upper limit values of the 90 vol. % distillationtemperature (T₉₀) and the final boiling point in distillation aredetermined in view of a high power generation quantity per weight, ahigh power generation quantity per CO₂ emission, a low fuel consumptionof a fuel cell system as a whole, a small THC in an exhaust gas, shortstarting time of a system, small deterioration of a reforming catalystto retain the initial properties, and the like.

Further, the 30 vol. % distillation temperature (T₃₀), 50 vol. %distillation temperature (T₅₀), and 70 vol. % distillation temperature(T₇₀) of the fuel of the invention are not particularly restricted,however, the 30 vol. % distillation temperature (T₃₀) is preferably 30°C. or higher and 60° C. or lower, the 50 vol. % distillation temperature(T₅₀) is preferably 35° C. or higher and 70° C. or lower, and the 70vol. % distillation temperature (T₇₀) is 35° C. or higher and 60° C. orlower.

Incidentally, the above-described initial boiling point (initial boilingpoint 0) in distillation, the 10 vol. % distillation temperature (T₁₀),the 30 vol. % distillation temperature (T₃₀), the 50 vol. % distillationtemperature (T₅₀), the 70 vol. % distillation temperature (T₇₀), the 90vol. % distillation temperature (T₉₀), and the final boiling point indistillation are distillation properties measured by JIS K 2254,“Petroleum products-Determination of distillation characteristics”.

Further, the content of sulfur in a fuel of the invention is notparticularly restricted, however, because deterioration of a fuel cellsystem comprising such as a reforming catalyst, a water gas shiftreaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks,and the like can be suppressed to low and the initial performances canbe maintained for a long duration, the content is preferably 50 ppm bymass or less, more preferably 30 ppm by mass or less, further morepreferably 10 ppm by mass or less, much further more preferably 1 ppm bymass or less, and most preferably 0.1 ppm by mass or less.

Here, sulfur means sulfur measured by JIS K 2541, “Crude Oil andPetroleum Products-Determination of sulfur content”, in case of 1 ppm bymass or more and means sulfur measured by ASTM D4045-96, “Standard TestMethod for Sulfur in Petroleum Products by Hydrogenolysis andRateometric Colorimetry” in the case of less than 1 ppm by mass.

In the invention, the respective contents of saturates, olefins andaromatics are not particularly restricted, however, saturates (V (S)),olefins (V (O)) and aromatics (V (Ar)) are preferably 30 vol. % or more,35 vol. % or less, and 50 vol. % or less, respectively based on thewhole hydrocarbons. Hereinafter, these compounds will separately bedescribed.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system, V (S) is preferably 30 vol. % or more, morepreferably 40 vol. % or more, further more preferably 50 vol. % or more,much further more preferably 60 vol. % or more, much further morepreferably 70 vol. % or more, much further more preferably 80 vol. % ormore, much further more preferably 90 vol. % or more, and mostpreferably 95 vol. % or more.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, small deterioration of a reformingcatalyst to maintain the initial performances for a long duration, and agood storage stability, V (O) is preferably 35 vol. % or less, morepreferably 25 vol. % or less, further more preferably 20 vol. % or less,much further more preferably 15 vol. % or less, and most preferably 10vol. % or less based on the whole hydrocarbons.

In view of a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission, a low fuel consumption of a fuelcell system as a whole, small THC in an exhaust gas, a short startingtime of the system, and small deterioration of a reforming catalyst tomaintain the initial performances for a long duration, V (Ar) ispreferably 50 vol. % or less, more preferably 45 vol. % or less, furthermore preferably 40 vol. % or less, much further more preferably 35 vol.% or less, much further more preferably 30 vol. % or less, much furthermore preferably 20 vol. % or less, much further more preferably 10 vol.% or less, and most preferably 5 vol. % or less.

Further, it is most preferable to satisfy the above-described preferableranges of sulfur and the above-described preferable ranges for thearomatics since deterioration of a reforming catalyst can be suppressedto low and the initial performances can be maintained for a longduration.

The values of the above-described V (S), V (O), and V (Ar) are allmeasured value according to the fluorescent indicator adsorption methodof JIS K 2536, “Liquid petroleum products-Testing method of components”.

Further, in the invention, the ratio of paraffins in saturates of a fuelis not particularly restricted, however, because of a high H₂ generationquantity, a high power generation quantity per weight, a high powergeneration quantity per CO₂ emission and the like, the ratio ofparaffins in saturates is preferably 60 vol. % or more, more preferably65 vol. % or more, further more preferably 70 vol. % or more, muchfurther more preferably 80 vol. % or more, much further more preferably85 vol. % or more, much further more preferably 90 vol. % or more, andmost preferably 95 vol. % or more.

The above-described saturates and paraffins are values quantitativelymeasured by the gas chromatography method mentioned above.

Further, the ratio of branched paraffins in the above-describedparaffins is not particularly restricted, however, the ratio of branchedparaffins in paraffins is preferably 30 vol. % or more, more preferably50 vol. % or more, and most preferably 70 vol. % or more because of ahigh power generation quantity per weight, a high power generationquantity per CO₂ emission, a low fuel consumption of a fuel cell systemas a whole, small THC in an exhaust gas, and a short starting time ofthe system.

The amounts of the above-described paraffin and branched-type paraffinare values quantitatively measured by the above-described gaschromatography.

Further, in the invention, the heat capacity of a fuel is notparticularly restricted, however, the heat capacity is preferably 2.6kJ/kg·° C. or less at 15° C. and 1 atm in liquid phase in view of a lowfuel consumption of a fuel cell system as a whole.

Further, in the invention, the heat of vaporization of a fuel is notparticularly restricted, the heat of vaporization is preferably 400kJ/kg or less in view of a low fuel consumption of a fuel cell system asa whole.

Those heat capacity and heat of vaporization can be calculated from thecontents of respective components quantitatively measured by theabove-described gas chromatography and the numeric values per unitweight of the respective components disclosed in “Technical DataBook-Petroleum Refining”, Vol. 1, Chap. 1, General Data, Table 1C1.

Further, in the invention, the Reid vapor pressure (RVP) of a fuel isnot particularly restricted, however, it is preferably 10 kPa or more inrelation to the power generation quantity per weight and preferably lessthan 100 kPa in relation to suppression of the amount of an evaporativegas (evapo-emission). It is more preferably 40 kPa or more and less than100 kPa and further more preferably 60 kPa or more and less than 100kPa. Here, the Reid vapor pressure (RVP) means the vapor pressure (Reidvapor pressure (RVP)) measured by JIS K 2258, “Testing Method for VaporPressure of Crude Oil and Products (Reid Method)”.

Further, in the invention, the research octane number (RON, the octanenumber by research method) is not particularly restricted, however, itis preferably 101.0 or less since deterioration of a reforming catalystcan be suppressed to low and the initial performances of a reformingcatalyst can be maintained for a long duration owing to a high powergeneration quantity per weight, a low fuel consumption of a fuel cellsystem as a whole, small THC in an exhaust gas, and a short startingtime of the system. Here, the octane number by research method (RON)means the research method octane number measured by JIS K 2280,“Petroleum products-Fuels-Determination of octane number, cetane numberand calculation of cetane number index”.

Further, in the invention, the oxidation stability of a fuel is notparticularly restricted, however, it is preferably 240 minutes or longerin view of storage stability. Here, the oxidation stability is theoxidation stability measured according to JIS K 2287, “Testing Methodfor Oxidation Stability of Gasoline (Induction Period Method)”.

Further, in the invention, the density of a fuel is not particularlyrestricted, however, it is preferably 0.78 g/cm³ or less sincedeterioration of a reforming catalyst can be suppressed to low and theinitial performances of a reforming catalyst can be maintained for along duration owing to small THC in an exhaust gas and a short startingtime of the system. Here, the density means the density measuredaccording to JIS K 2249, “Crude petroleum and petroleumproducts-Determination of density and petroleum measurement tables basedon a reference temperature (15° C.)”.

A production method for the fuel of the invention is not particularlyrestricted. Practical method is, for example, the fuel can be preparedby blending one or more kinds of oxygenates, and further by blendinghydrocarbons at need.

As for hydrocarbons, for example, the hydrocarbons can be produced byusing one or more kinds of the following hydrocarbon base materials;light naphtha obtained by the atmospheric distillation of crude oil,heavy naphtha obtained by the atmospheric distillation of crude oil,desulfurized light naphtha obtained by desulfurization of light naphtha,desulfurized heavy naphtha obtained by desulfurization of heavy naphtha,isomerate obtained by converting light naphtha into isoparaffins by anisomerization process, alkylate obtained by the addition reaction(alkylation) of low molecule weight olefins to hydrocarbons such asisobutane, desulfurized alkylate obtained by desulfurizing alkylate, lowsulfur alkylate produced from desulfurized hydrocarbons such asisobutane and desulfurized low molecule weight olefins, reformateobtained by catalytic reforming, raffinate which is residue afterextraction of aromatics from distillate of reformate, light distillateof reformate, middle to heavy distillate of reformate, heavy distillateof reformate, cracked gasoline obtained by catalytic cracking orhydrocracking process, light distillate of cracked gasoline, heavydiatillate-cracked gasoline, desulfurized cracked gasoline obtained bydesulfurizing cracked gasoline, desulfurized light distillate of crackedgasoline obtained by desulfurizing light distillate of cracked gasoline,desulfurized heavy distillate of cracked gasoline obtained bydesulfurizing heavy distillate of cracked gasoline, a light distillateof “GTL (Gas to Liquids)” obtained by F-T (Fischer-Tropsch) synthesisafter cracking natural gas or the like to carbon monoxide and hydrogen,desulfurized LPG obtained by desulfurizing LPG, and the like. Thehydrocarbons can also be produced by desulfurizing by hydrogenating oradsorption after mixing one or more kinds of the above base materials.

Among them, preferable materials as the base materials for theproduction of the fuel of the invention are light naphtha, desulfurizedlight naphtha, isomerate, desulfurized alkylates obtained bydesulfurizing alkylates, low sulfur alkylates produced from desulfurizedhydrocarbons such as isobutane and desulfurized low molecule weightolefins, desulfurized light distillate of cracked gasoline obtained bydesulfurizing a light distillate of cracked gasoline, a light distillateof GTL, desulfurized LPG obtained by desulfurizing LPG, and the like.

A fuel for a fuel cell system of the invention may comprise additivessuch as dyes for identification, oxidation inhibitors for improvement ofoxidation stability, metal deactivators, corrosion inhibitors forcorrosion prevention, detergents for keeping cleanness of a fuel system,lubricity improvers for improvement of lubricating property and thelike.

However, since a reforming catalyst is to be scarcely deteriorated andthe initial performances are to be maintained for a long duration, theamount of dyes is preferably 10 ppm or less and more preferably 5 ppm orless. For the same reasons, the amount of oxidation inhibitors ispreferably 300 ppm or less, more preferably 200 ppm or less, furthermore preferably 100 ppm or less, and most preferably 10 ppm or less. Forthe same reasons, the amount of metal deactivators is preferably 50 ppmor less, more preferably 30 ppm or less, further more preferably 10 ppmor less, and most preferably 5 ppm or less. Further, similarly since areforming catalyst is to be scarcely deteriorated and the initialperformances are to be maintained for a long duration, the amount ofcorrosion inhibitors is preferably 50 ppm or less, more preferably 30ppm or less, further more preferably 10 ppm or less, and most preferably5 ppm or less. For the same reasons, the amount of detergents ispreferably 300 ppm or less, more preferably 200 ppm or less, and mostpreferably 100 ppm or less. For the same reasons, the amount oflubricity improvers is preferably 300 ppm or less, more preferably 200ppm or less, and most preferably 100 ppm or less.

A fuel of the invention is to be employed as a fuel for a fuel cellsystem. A fuel cell system mentioned herein comprises a reformer for afuel, a carbon monoxide conversion apparatus, fuel cells and the like,however, a fuel of the invention may be suitable for any fuel cellsystem.

The reformer is an apparatus for obtaining hydrogen, by reforming afuel. Practical examples of the reformer are:

(1) a steam reforming type reformer for obtaining products of mainlyhydrogen by treating a heated and vaporized fuel and steam with acatalyst such as copper, nickel, platinum, ruthenium and the like;

(2) a partial oxidation type reformer for obtaining products of mainlyhydrogen by treating a heated and vaporized fuel and air with or withouta catalyst such as copper, nickel, platinum, ruthenium and the like; and

(3) an auto thermal reforming type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel, steam and air,which carries out the partial oxidation of (2) in the prior stage andcarries out the steam type reforming of (1) in the posterior stage whileusing the generated heat of the partial oxidation reaction with acatalyst such as copper, nickel, platinum, ruthenium and the like.

The carbon monoxide conversion apparatus is an apparatus for removingcarbon monoxide which is contained in a gas produced by theabove-described reformer and becomes a catalyst poison in a fuel celland practical examples thereof are:

(1) a water gas shift reactor for obtaining carbon dioxide and hydrogenas products from carbon monoxide and steam by reacting a reformed gasand steam in the presence of a catalyst of such as copper, nickel,platinum, ruthenium and the like; and

(2) a preferential oxidation reactor for converting carbon monoxide intocarbon dioxide by reacting a reformed gas and compressed air in thepresence of a catalyst of such as platinum, ruthenium and the like, andthese are used singly or jointly.

As a fuel cell, practical examples are a proton exchange membrane typefuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a moltencarbonate type fuel cell (MCFC), a solid oxide type fell cell (SOFC) andthe like.

Further, the above-described fuel cell system can be employed for anelectric automobile, a hybrid automobile comprising a conventionalengine and electric power, a portable power source, a dispersion typepower source, a power source for domestic use, a cogeneration system andthe like.

EXAMPLES

The properties of base materials employed for the respective fuels forexamples and comparative examples are shown in Table 1.

Also, the properties of the respective fuels employed for examples andcomparative examples are shown in Table 2.

TABLE 1 desulfurized light isomerate naphtha *1 *2 MTBE sulfur 0.1 0.30.1 hydrocarbon ratio carbon number: C₄ vol. % 5.4 2.4 — carbon number:C₅ vol. % 42.2 43.6 — carbon number: C₆ vol. % 49.2 53.6 — carbonnumber: C₇ vol. % 3.1 0.3 — carbon number: C₈ vol. % 0.1 0.1 — carbonnumber: C₉ vol. % 0.0 0.0 — carbon number: C₁₀₊ vol. % 0.0 0.0 —composition saturates vol. % 98.9 99.9 — olefins vol. % 0.0 0.1 —aromatics vol. % 1.1 0.0 — paraffins in saturates vol. % 92.6 98.4 —branched paraffins in vol. % 37.2 83.5 — paraffins oxygen mass % 0.0 0.018.2 distillation initial boiling point ° C. 28.0 32.0 55.0 10% point °C. 40.5 40.5 — 30% point ° C. 47.5 43.5 — 50% point ° C. 51.5 46.5 — 70%point ° C. 57.5 51.0 — 90% point ° C. 68.5 58.5 — final boiling point °C. 78.5 70.0 — heat capacity kJ/kg · ° C. 2.197 2.197 2.075 (liquid)heat capacity (gas) kJ/kg · ° C. 1.569 1.582 1.477 heat of vaporizationkJ/kg 344.4 332.8 319.7 RVP kPa 95.6 91.0 53.0 research octane 71.8 81.8118.0 number oxidation stability min. >1440 >1440 — density g/cm³ 0.65640.6475 0.7456 net heat of kJ/kg 44819 44798 35171 combustion ethanolmethanol DME *3 sulfur 0.1 0.1 0.1 hydrocarbon ratio carbon number: C₄vol. % — — — carbon number: C₅ vol. % — — — carbon number: C₆ vol. % — —— carbon number: C₇ vol. % — — — carbon number: C₈ vol. % — — — carbonnumber: C₉ vol. % — — — carbon number: C₁₀₊ vol. % — — — compositionsaturates vol. % — — — olefins vol. % — — — aromatics vol. % — — —paraffins in saturates vol. % — — — branched paraffins in vol. % — — —paraffins oxygen mass % 34.8 49.9 34.8 distillation initial boilingpoint ° C. 78.0 64.7 −25.0 10% point ° C. — — — 30% point ° C. — — — 50%point ° C. — — — 70% point ° C. — — — 90% point ° C. — — — final boilingpoint ° C. — — — heat capacity kJ/kg · ° C. 2.339 2.456 2.510 (liquid)heat capacity (gas) kJ/kg · ° C. 1.381 1.343 1.389 heat of vaporizationkJ/kg 855.6 1096.8 467.8 RVP kPa 15.9 30.0 843.2 research octane 130.0110.0 — number oxidation stability min. — — density g/cm³ 0.7963 0.79610.6709 net heat of kJ/kg 26824 19916 28840 combustion *1: lightfractions obtained by further distilling desulfurized full-range naphtha*2: gasoline fractions obtained by treating desulfurized light naphthawith an isomerization process *3: dimethyl ether

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Mixing desulfurized light naphtha 85%ratio isomerate 95% methanol 5% ethanol 100% MTBE 15% 100% DMEProperties Sulfur ppm by mass 0.1 0.3 0.1 0.1 ratio by carbon numbercarbon number: C₄ vol. % 54 2.4 0.0 0.0 carbon number: C₅ vol. % 42.243.6 0.0 0.0 carbon number: C₆ vol. % 49.2 53.6 0.0 0.0 carbon number:C₇ vol. % 3.1 0.3 0.0 0.0 carbon number: C₈ vol. % 0.1 0.1 0.0 0.0carbon number: C₇ + C₈ vol. % 3.2 0.4 0.0 0.0 carbon number: C₉ vol. %0.0 0.0 0.0 0.0 carbon number: C₁₀₊ vol. % 0.0 0.0 0.0 0.0 Compositionin hydrocarbons saturates vol. % 98.9 99.9 0.0 0.0 olefins vol. % 0.00.1 0.0 0.0 aromatics vol. % 1.1 0.0 0.0 0.0 paraffins in saturates vol.% 92.6 98.4 0.0 0.0 branched paraffins in vol. % 37.2 83.5 0.0 0.0paraffins oxygen mass % 3.0 3.0 18.2 34.8 Density g/cm³ 0.6698 0.65490.7456 0.7963 Distillation properties initial boiling point ° C. 28.032.0 55.0 78.0 10% point ° C. 40.5 40.5 — — 30% point ° C. 49.5 43.5 — —50% point ° C. 53.5 45.5 — — 70% point ° C. 55.5 50.5 — — 90% point ° C.67.0 59.5 — — final boiling point ° C. 84.5 79.0 — — Reid vapor pressurekPa 81 106 — — Research octane number 79.8 85.8 — — Oxidation stabilitymin. 1440 or more 1440 or more — — net heat of combustion kJ/kg 4321043290 35171 26824 Heat capacity (liquid) kJ/kg · ° C. 2.176 2.212 2.0752.339 Heat capacity (gas) kJ/kg · ° C. 1.554 1.567 1.477 1.381 Heat ofvaporization kJ/kg 340.2 379.3 319.7 755.6 Ex. 5 Comp. Ex. 1 Comp. Ex. 2Mixing desulfurized light naphtha 100% ratio isomerate methanol 100%ethanol MTBE DME 100% Properties Sulfur ppm by mass 0.1 0.1 0.1 ratio bycarbon number carbon number: C₄ vol. % 0.0 54 0.0 carbon number: C₅ vol.% 0.0 42.2 0.0 carbon number: C₆ vol. % 0.0 49.2 0.0 carbon number: C₇vol. % 0.0 3.1 0.0 carbon number: C₈ vol. % 0.0 0.1 0.0 carbon number:C₇ + C₈ vol. % 0.0 3.2 0.0 carbon number: C₉ vol. % 0.0 0.0 0.0 carbonnumber: C₁₀₊ vol. % 0.0 0.0 0.0 Composition in hydrocarbons saturatesvol. % 0.0 98.9 0.0 olefins vol. % 0.0 0.0 0.0 aromatics vol. % 0.0 1.10.0 paraffins in saturates vol. % 0.0 92.6 0.0 branched paraffins invol. % 0.0 37.2 0.0 paraffins oxygen mass % 34.8 0.0 49.9 Density g/cm³0.6709 0.6564 0.7961 Distillation properties initial boiling point ° C.−25.0 28.0 65.0 10% point ° C. — 40.5 — 30% point ° C. — 47.5 — 50%point ° C. — 51.5 — 70% point ° C. — 57.5 — 90% point ° C. — 68.5 —final boiling point ° C. — 88.5 — Reid vapor pressure kPa — 89 —Research octane number — 71.8 — Oxidation stability min. — 1350 — netheat of combustion kJ/kg 28840 44820 19916 Heat capacity (liquid) kJ/kg· ° C. 2.510 2.197 2.456 Heat capacity (gas) kJ/kg · ° C. 1.389 1.5691.343 Heat of vaporization kJ/kg 467.8 344.4 1096.8

These respective fuels were subjected to a fuel cell system evaluationtest, an evaporative gas test, and a storage stability test.

Fuel Cell System Evaluation Test

(1) Steam Reforming

A fuel and water were evaporated by electric heating and led to areformer filled with a noble metal type catalyst and kept at aprescribed temperature by an electric heater to generate a reformed gasenriched with hydrogen.

The temperature of the reformer was adjusted to be the minimumtemperature (the minimum temperature at which no THC was contained in areformed gas) at which reforming was completely carried out in aninitial stage of the test.

Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a steam reforming type fuel cell system employed for theevaluation was illustrated in FIG. 1.

(2) Partial Oxidation

A fuel is evaporated by electric heating and together with air, theevaporated fuel was led to a reformer filled with a noble metal typecatalyst and kept at a 1100° C. by an electric heater to generate areformed gas enriched with hydrogen.

Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

A flow chart of a partial oxidation type fuel cell system employed forthe evaluation was illustrated in FIG. 2.

(3) Evaluation Method

The amounts of H₂, CO, CO₂ and THC in the reformed gas generated from areformer were measured immediately after starting of the evaluationtest. Similarly, the amounts of H₂, CO, CO₂ and THC in the reformed gasgenerated from a carbon monoxide conversion apparatus were measuredimmediately after starting of the evaluation test.

The power generation quantity, the fuel consumption, and the CO₂ amountemitted out of a fuel cell were measured immediately after starting ofthe evaluation test and 100 hours later from the starting.

The energy (preheating quantities) necessary to heat the respectivefuels to a prescribed reforming temperature were calculated from theheat capacities and the heat of vaporization.

Further, these measured values, calculated values and the heating valuesof respective fuels were employed for calculation of the performancedeterioration ratio of a reforming catalyst (the power generation amountafter 100 hours later from the starting divided by the power generationamount immediately after the starting), the thermal efficiency (thepower generation amount immediately after the starting divided by thenet heat of combustion of a fuel), and the preheating energy ratio(preheating energy divided by the power generation amount).

Evaporative Gas Test

A hose for filling a sample was attached to a fuel supply port of a 20liter portable gasoline can and the installation part was completelysealed. While an air venting valve of the can being opened, 5 liter ofeach fuel was loaded. On completion of the loading, the air ventingvalve was closed and the can was left still for 30 minutes. After thecan being kept still, an activated carbon adsorption apparatus wasattached to the air venting valve and the valve was opened. Immediately,10 liter of each fuel was supplied from the fuel supply port. After 5minutes of the fuel supply, while the air releasing valve being openedand kept as it was, the vapor was absorbed in the activated carbon andafter that, the weight increase of the activated carbon was measured.Incidentally, the test was carried out at a constant temperature of 25°C.

Storage Stability Test

A pressure resistant closed container was filled with each fuel andoxygen, heated to 100° C. and while the temperature being kept as itwas, the container was kept still for 24 hours. Evaluation was carriedout according to “Petroleum products—Motor gasoline and aviationfuels—Determination of existent gum” defined as JIS K 2261.

The respective measured values and the calculated values are shown inTable 3.

TABLE 3 EX. 1 EX. 2 EX. 3 EX. 4 Evaluation results Electric powergeneration by steam reforming method (reforming temperature = optimumreforming temperature 1)) Optimum ° C. 620 610 440 405 reformingtemperature Electric energy kJ/fuel kg initial performance 29370 2953024920 20860 100 hours later 29350 29500 24900 20850 performance 100hours later 0.07% 0.10% 0.08% 0.05% deterioration ratio Thermalefficiency 2) initial performance 68% 68% 71% 78% CO₂ generation kg/fuelkg initial performance 2.970 2.956 2.496 1.911 Energy per CO₂ KJ/CO₂-kginitial performance 9889 9990 9984 10916 Preheating energy kJ/fuel kg1281 1309 950 1431 3) Preheating energy 4.4% 4.4% 3.8% 6.9% ratio 4)Electric power generation by partial oxidation reforming method(reforming temperature 1100° C.) Electric energy kJ/fuel kg initialperformance 14550 14770 12460 11320 100 hours later 14540 14750 1245011310 performance 100 hours later 0.07% 0.14% 0.08% 0.09% deteriorationratio Thermal efficiency 2) initial performance 34% 34% 35% 42% CO₂generation kg/fuel kg initial performance 2.972 2.958 2.498 1.912 Energyper CO₂ KJ/CO₂-kg initial performance 4896 4993 4988 5921 Preheatingenergy kJ/fuel kg 2026 2077 1925 2391 3) Preheating energy 13.9% 14.1%15.4% 21.1% ratio 4) Evaporative gas test Evaporative gas g/test 18.128.9 5.9 — Storage stability test Washed existent mg/100 ml 1 1 1 — gumEX. 5 Comp. Ex. 1 Comp. Ex. 2 Evaluation results Electric powergeneration by steam reforming method (reforming temperature = optimumreforming temperature 1)) Optimum reforming ° C. 320 680 300 temperatureElectric energy kJ/fuel kg initial performance 20850 30260 17140 100hours later 20840 30240 17130 performance 100 hours later 0.05% 0.07%0.06% deterioration ratio Thermal efficiency 2) initial performance 72%68% 86% CO₂ generation kg/fuel kg initial performance 1.912 3.064 1.374Energy per CO₂ KJ/CO₂-kg initial performance 10905 9876 12475 Preheatingenergy 3) kJ/fuel kg 410 1391 1484 Preheating energy 2.0% 4.6% 8.7%ratio 4) Electric power generation by partial oxidation reforming method(reforming temperature 1100° C.) Electric energy kJ/fuel kg initialperformance 11330 14970 10280 100 hours later 11320 14950 10270performance 100 hours later 0.09% 0.13% 0.10% deterioration ratioThermal efficiency 2) initial performance 39% 33% 52% CO₂ generationkg/fuel kg initial performance 1.910 3.065 1.374 Energy per CO₂KJ/CO₂-kg initial performance 5932 4884 7482 Preheating energy 3)kJ/fuel kg 1493 2047 2585 Preheating energy 13.2% 13.7% 25.1% ratio 4)Evaporative gas test Evaporative gas g/test — 21.5 — Storage stabilitytest Washed existent mg/100 ml — 2 — gum 1) the minimum temperature atwhich no THC is contained in a reformed gas 2) electric energy/net heatof combustion of fuel 3) energy necessary for heating a fuel to areforming temperature 4) preheating energy/electric energy

INDUSTRIAL APPLICABILITY

As described above, a fuel for a fuel cell system of the inventioncomprising a specific amount of oxygenates has performances with smalldeterioration and can provide high output of electric energy and otherthan that, the fuel can satisfy a variety of performances for a fuelcell system.

What is claimed is:
 1. A fuel for a fuel cell system comprising 0.5-40mass % of oxygenates in terms of an oxygen content based on the wholefuel, wherein the fuel contains 5 vol. % or more of hydrocarbons basedon the whole fuel, a content of hydrocarbon compounds having 4 carbonatoms is 15 vol. % or less, a content of hydrocarbon compounds having 5carbon atoms is 5 vol. % or more and a content of hydrocarbon compoundshaving 6 carbon atoms is 10 vol. % or more based on the wholehydrocarbons, a sulfur content is 1 ppm by mass or less based on thewhole fuel, saturates are 30 vol. % or more based on the wholehydrocarbons, a ratio of branched paraffins in paraffins is 30 vol. % ormore, heat capacity of the fuel is 2.6 kJ/kg ° C. or less at 15° C. and1 atm in liquid phase, heat of vaporization of the fuel is 400 kJ/kg orless, said fuel has distillation properties of an initial boiling pointin distillation of 24° C. or higher and 40° C. or lower, a 10 vol. %distillation temperature (T₁₀) of 25° C. or higher and 50° C. or lower,a 90 vol. % distillation temperature (T₉₀) of 45° C. or higher and 100°C. or lower, and a final boiling point in distillation of 55° C. orhigher and 130° C. or lower.
 2. A fuel for a fuel cell system accordingto claim 1, wherein olefins are 35 vol. % or less based on the wholehydrocarbons.
 3. A fuel for a fuel cell system according to claim 1,wherein aromatics are 50 vol. % or less based on the whole hydrocarbons.4. A fuel for a fuel cell system according to claim 1, wherein Reidvapor pressure of the fuel is 10 kPa or more and less than 100 kPa.
 5. Afuel for a fuel cell system according to claim 1, wherein researchoctane number of the fuel is 101.0 or less.
 6. A fuel for a fuel cellsystem according to claim 1, wherein oxidation stability of the fuel is240 minutes or longer.
 7. A fuel for a fuel cell system according toclaim 1, wherein density of the fuel is 0.78 g/cm³ or less.